1. Field
Example embodiments relate to a copolymer, an organic insulating layer composition, an organic insulating layer and an organic thin film transistor manufactured using the same. Other example embodiments relate to a copolymer, which includes side chains which may decrease the surface energy of an insulating layer, thereby improving the alignment of a semiconductor material, and side chains including photoreactive functional groups having an increased degree of cross-linking, thereby improving the characteristics of an organic thin film transistor manufactured using the same, an organic insulating layer composition including the same, and an organic insulating layer and an organic thin film transistor manufactured using the same.
2. Description of the Related Art
An Organic Thin Film Transistor (OTFT) may be used as a switching device for controlling the operation of each pixel of a device for driving each pixel in a flat-panel display, e.g., a liquid crystal display (LCD) and/or an electroluminescent display (ELD). The organic thin film transistor may be used for a smart card and/or a plastic chip for an inventory tag.
This organic thin film transistor may include a semiconductor layer having a source region and a drain region doped with an increased concentration of impurities and a channel region formed therebetween. Further, the organic thin film transistor may be configured to include a gate electrode which is insulated from the semiconductor layer and located in a region corresponding to the channel region, and a source electrode and drain electrode, which are respectively in contact with the source region and the drain region.
In initial research into an organic thin film transistor (OTFT), conventional silicon-based inorganic insulator materials, e.g., SiOx and/or SiNx, were used as insulating layers. However, as larger sized, inexpensive and flexible displays have been required, there is more demand for organic insulator materials, rather than inorganic insulator materials. Commonly usable polymer materials, e.g., polyvinylalcohol, polyvinylphenol and/or polymethylmethacrylate, have been used as a gate insulating layer of an organic thin film transistor. These polymer materials may be formed into an insulating layer through a relatively low-cost processes, e.g., spin coating, but there may be difficulty in effectively controlling the interaction between the polymer materials and organic semiconductor molecules to thus improve the performance thereof.
For example, the related art discloses an organic thin film transistor in which the driving voltage and threshold voltage thereof are decreased using a high dielectric constant insulating layer. A gate insulating layer may be formed using inorganic metal oxides, e.g., BaxSr1-xTiO3 (BST; Barium Strontium Titanate), Ta2O5, Y2O3 and/or TiO2, or ferroelectric insulating materials, e.g., PbZrxTi1-xO3(PZT), Bi4Ti3O12, BaMgF4, SrBi2(Ta1-xNbx)2O9, Ba (Zr1-xTix)O3 (BZT), BaTiO3, SrTiO3 and/or Bi4Ti3O12, through a chemical vapor deposition, physical vapor deposition, sputtering and/or sol-gel coating method. According to the related art, driving voltage may be decreased, but charge mobility may not be as high as before, and most manufacturing processes may be performed at an increased temperature of about 200° C.˜about 400° C., so that plastic substrates, for flexible displays, may not be used. General wet processes, e.g., a simple coating or printing, may be difficult to use at the time of manufacturing devices.
In an organic thin film transistor, because the surface characteristics of an insulating layer have an influence on the improvement of the performance of an organic thin film transistor, various research on a gate insulating layer, which may increase the degree of charge transport on the surface between a gate insulating layer and an organic semiconductor layer and may be formed through a simpler process, is being conducted. As the surface energy of an insulating layer is lowered, for example, the insulating layer may exhibit relatively strong hydrophobicity, and the alignment of a semiconductor material in an organic semiconductor layer may be improved, thereby realizing improved transistor performance. Accordingly, attempts have been made to improve the degree of charge transport by surface-treating an insulating layer. However, in these attempts, because additional surface-treatment must be performed, overall processibility may decrease, and costs may increase.
The organic thin film transistor, manufactured using an organic insulator, may cause hysteresis at the time of driving the organic thin film transistor because charges may be trapped and accumulated between a semiconductor and an insulator, or the organic insulator may absorb moisture due to water in the air. Due to such hysteresis, occurring at the time of driving the organic thin film transistor, use of the organic thin film transistor for actual displays and logic devices may be difficult, even if desired electrical characteristics are exhibited.